The present invention relates to generators for use in micro-electro-mechanical systems, and particularly to a micro-electro-mechanical generator for generating electricity by using energy from bubble growth generated in liquid by a heat source, such as body heat from a human being.
A generator using a heat source having a temperature similar to body temperature, may serve as a power source for bio-micro-electro-mechanical equipment such as blood sugar level monitoring devices, blood pressure monitors, drug dosage units, artificial organs, micro robots for surgical operation, etc., in micro-electro-mechanical systems (MEMS). These generators may use heat emitted from a CPU, so that they can serve as a cooling device for subminiature electronic appliances having a CPU or general electricity-reproduction apparatuses for MEMS.
Currently under-way studies on generators for MEMS are conducted mainly by academic groups and broadly divided into studies on combustion systems which burn liquid combustibles such as hydrocarbon based fuel to generate electricity, studies on thermoelectric elements, and study on fuel cells.
Attempts to develop a combustion system include a study on micro gas turbines having a diameter of about 10 mm, thickness of 3 mm, weight of 1 g and electric power capacity of 16 W generated by burning fuel at a rate of 7 g per hour, and a study on internal combustion engines having a volume of 8 cubic mm, are under way.
Power generation systems employing thermoelectric elements use the Peltier Effect and are based on electromotive force generated when different temperature conditions are applied to two materials. Some of the development groups have been trying to provide thermoelectric elements with different temperature conditions, in which the high temperature condition is obtained by fuel combustion.
The fuel cell is a known device in which electrical energy is generated using hydrogen, oxygen, a proton exchange membrane, etc., while water is obtained as a byproduct. This device has been used in macro scale systems. Recently, studies are under way to allow this type of device to be available in the MEMS.
The studies described above, however, have not yet developed conspicuous results in the art and even if they develop practical results, the results may have a limited applicable field as most are adapted to use a heat source having a very high temperature.
It is, therefore, a main object of the present invention to provide a micro-electro-mechanical generator using a heat source having a relatively low temperature, e.g. body temperature.
Another object of the present invention is to provide a micro-electro-mechanical generator which does not need a separate energy source for power generation and avoids periodic re-supply or frequent replacement.
These objects and other objects, which will become apparent to those skilled in the art, are accomplished with a micro-electro-mechanical generator comprising a liquid chamber further comprised and defined by bottom blocks and side walls. The chamber is adapted to confine a liquid therein. A bubble generation means for generating bubbles is disposed within the liquid chamber. The micro-electro-mechanical generator also has elastic piezoelectric plates, each of which is further comprised of a piezoelectric material layer, and a first and a second ends. The piezoelectric material layer is positioned in the liquid chamber adjacent to the upper portion of the bubble generation means. The elongated elastic piezoelectric plate deforms with contact with the generated bubbles, and the first end of the elongated elastic piezoelectric plate is a free end, while the second end of the elongated elastic piezoelectric plate is a fixed end. A pair of electrodes are electrically connected to the piezoelectric material layer.
The micro-electro-mechanical generator may also have a heat sinking means formed on an upper surface of the liquid chamber. The bubble generation means is a metal block forming at least a portion of the bottom blocks of the liquid chamber, and thermally connected to a heat source. The remaining portions of the bottom blocks other than the metal block can be made of a thermal insulation material. The second end of the elongated elastic piezoelectric plate is fixed to one of the side walls. The side walls of the liquid chamber are made of a thermal insulation material. The micro-electro-mechanical generator may also have an electric capacitor electrically connected to the pair of electrodes.